Some displays require setting AUS mode in the LDCD AUS Mode ControlRegister to work with the imxfb driver. Like the value of the PanelConfiguration Register, the AUS mode setting depends on the displaymode.

Allow setting AUS mode from the device tree by adding a booleanproperty. Make this property optional to keep the DT ABI stable.AUS mode can be set only on imx21 and compatible chipsets.

Signed-off-by: Martin Kaiser <martin@kaiser.cx>---re-sending v3, rebased against current linux-nextit seems this got lost along the way, there was a bit of confusionwhether to split this in two patches or not

v3: use a boolean DT property instead of the register value separate patches for DT binding and code changes